Toning and intensifying solutions



' Patented May 16, 1939 Tome AND m'rnnsmmo SOLUTIONS Kenneth c. n. Hickman and John 0. Becker, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. E, a corporation of New Jersey No Drawing. Application March 9, 1938,

' Serial No. 194,899

This invention relates to toning and intensifying solutions for developed photographic images,

whether in the form of negatives or prints, and

- more particularly to a new type of single solution toning and intensifying bath.

This application is in part a continuation of our 'copending application Serial No. 722,730,

filed April 27, 1934.-

As is well known, silver salts will react with other soluble salts, but metallic silver is attacked most readily by elementary substances or their equivalents. It is for this reason that one of the best known methods of sulfide toning involves first, the conversion of the metallic silver'to a salt, such as silver bromide and potassium ferricyanide and, second, the conversion of the silver bromide to silver sulfide bydouble decomposition with sodium sulfide. This particular conversion,

however, cannot be made in one stage in a single 20 solution because the ferricyanide attacks the sodium sulfide more readily than the silver. The problem is then to find an oxidizing agent sufficiently powerful to' oxidize the silver and yet be compatible with the sulfiding agent. A number of single solution sulfide toning processes have been developed to solve this problem, but

which will meet many of the requirements of such baths without at the same time possessing the limitations of the hitherto known solutions. 40 A further" object is to provide a single solution bath which may not only be used for toning the image, but also for intensification: A' still fur-' ther object is to provide a bath of this type pos-, sessing the novel property that it, may be employed for toning a photographic image immediately after development and before fixing.

-With the above and other objects in view which will become apparent as'the description proceeds, we have set forth our invention in the following 50 specification and examples which are included merely for purposes of illustration and not as av limitation thereof. b

. We have discovered that various soluble thio- 5' sulfates may be employed for the toning and in- It is the principal object of the present invention to provide a single solution toning bath.

tensification of silver images. These compounds are characterized by the fact that they all contain available sulfur in their di-valent condition. Many othe't substances contain di-valent sulfur, mostly thioureas and the polysulfides, but in such compounds the di-valent sulfur is connected to an unlike atom or to another unsaturated sulfur atom. The di-valent sulfur in the class of compounds considered within the scopeof this invention is connected by one or two bonds to another sulfur atom, which latter atom is otherwise fully oxygenated and is in itshexa-valent condition. We shall discuss herein the thicsulfate derivatives, in particular the compounds I of thiosulfuric acid and organic substances containing a quinone or hydroquinone grouping. In these discussions we shall .refer to some of the broader theoretical aspects'of our discovery, al-

though we are not to be understood as in; any way limiting our invention thereby.

We have found that the silver salts of certain of these organic thiosulfuric acid derivatives readily eliminate silver sulfide. This is of especial importance, since in order to be suitable for use, in a toning solution, the toning agent must be of the kind which will produce a silver salt which will readily decompose into silver sulfide as fast as the metallic silver is oxidized, as otherwise the image will wander or suffer reduction. Specifically we have found that they possess at i one and the same time a greater, instability toward acid and oxidizing agents and a greater stability toward silver with the result that their silver salts, which are more easily-formed, are also more easily broken up, depositing silver sulfide, and therefore that such derivatives may be employed .as toners with excellent results.

Among these derivatives may be mentioned the quinone and hydroquinone derivatives of thinsulfuric acid. Of the hydroquinone compounds, hydroquinone monothiosulfuric acid, hydroquinone dith iosulfuric acid and hydroquinone tetrathiosulfuric acid may all be formed by the reaction of a thiosulfate and quinoneunder controlled conditions. The conditions are not dimcult to obtain and the acids are all easily prepared; the "mono form resulting from dnopping quinone dissolved in dilute acetic acid into ordinary hypo, the "di form by adding hypo to quinone'in acetic acid, while the tetra form separates in almost theoretical yield when solutions of chromic acid and hypo are added simultaneously to a solution 'of quinone in acetic acid.

These three hydroquinone thiosulfuric acids are Hydroqulnone monothicsulfurio acid .SOIH

Hydroquinone dithiosuliuric acid H803. .SOlH

Hydroquinons tetrathicsulfuric acid veloping out papers according to our invention, has the following composition:

Hydroquinone tetrathiosulfuric acid- 4.--- Quinone g.--- 1.0 Sulfuric acid cc. .25 Water or 100.00

The above bath can be used continuously until the concentration of hydroquinone produced in the toning reaction becomes so high that an equilibrium mixture results which is non-reactive. The activity of the bath can then be restored, by adding chromic acid, although the rejuvenated bath stains slightly from dyes produced by secondary oxidation.

A toning bath containing as much as 1 per cent of free mineral acid may have a somewhat harmful effect on gelatine emulsions. Therefore, films and prints to be intensified in such a bath should be fixed in hypo containing alum and the toning solution should likewise be loaded with alum. Bearing in mind that hydroquinone is a product of the toning reaction, the toning solution in use may contain, in accordance with our invention, a quinone thiosulfuric acid, 'a hydroquinone, a mineral acid, and an alum, for example, chrome alum, potassium chromium sulfate. Such a solution containing chiefly the monoand di-thiosulfuric acids, which confer both toning and intensifying properties may be made by mixing hydroquinone, chromic acid, and hypo-chemicals which are readily available in the photographic laboratory. Inasmuch as the toning solution does not keep well, its constituents should be bottled separately, a convenient recipe being as follows:

Solution A Water r c 500 Potassium 'dichromate g. 16

Sulfuric acid (conc.) g.

. ing place with the mono and tetra forms of Solution B Water 0 n 500 Hydroquinone g. 16 Sodium bisulphite g. .75

Solution 0 Water 0 c 500 Hypo g. 11 Solution C' I Water 0 c 350 Hypo g 80 Equal portions of the first three solutions are 4 employed, B being poured into A in a thin stream with rapid stirring, after which C is added to the mixture, also with stirring. The resulting solution is then cooled down to below 70 F. for use.

If a quicker bath is needed, one tenth the volume of Solution 0' may replace Solution C. A very vigorous bath may, for example, have the following formula:

Hydroquinone dithiosulfuric acid.. g. .5 Quinone g. 1.0 Sulfuric acid g. .25

Water m 100.00

This solution should be used at about 65-75" F.

An example of a toning bath containing hydroquinone monothiosulfuric acid has the following composition:

Quinone g. 1.0 Water 0 Sulfuric acid 0 Hydroquinone monothiosulfuric' acid (conveniently in the form of its potassium salt) g.

This toning solution produces a reddish-purple tone which can be varied by varying the quantity of the hydroquinone salt as desired.

While we do not wish to confine ourselves to any particular theory or explanation of the mechanism involved in the various reactions in toning by means of these hydroquinone thiosulfuric acids, we believe that the first product of toning is not silver sulfide, but a silver hydrothe hydroquinone thiosulfuric'acid are, we believe, similar to those occurring with the 411" form. The first stage in all the reactions is a bleaching of the image by virtue of formation of the silver salt of thqhydroquinone acid employed. The second stage is the darkening of this compound by other substances in solution, the first development of color, probably being due to the formation of a quinhydrone. The third stage is a process occurring simultaneously with the other two, but at a rate varying with the nature of the solution, being the splitting ofl of silver sulfide from the silver thiosulfate chain. One of the remarkable properties of our tonin baths is that they can be adapted to tone the 

